The invention concerns a method for calculating the travel of a band-shaped superconductor in a coil section of a high field magnet coil through a transition region towards or away from the coil section, wherein the coil section is wound onto a cylindrical coil body in the shape of a solenoid.
A high field magnet coil with conventional conductor guidance is disclosed e.g. in “Supraleitende Magnete für die NMR-Spektroskopie” (superconducting magnet for NMR spectroscopy) by Rainer Haeβner, TU Munich, 21.12.2001, URL:http://www.org.chemie.tu-muenchen.de/people/rh/nmrueb/magnet2.pdf (see FIGS. 2 and 5).
Superconducting magnet coils are used for producing maximum magnetic field strengths, in particular for NMR (nuclear magnetic resonance) applications. Superconductors can carry electric current without loss within certain temperature ranges, magnetic field strength ranges and current strength ranges to thereby produce highly constant magnetic fields. High-temperature superconductors (HTSC), i.e. superconductors with a transition temperature above the boiling point of liquid nitrogen, are particularly suitable for magnet construction and can generate particularly high magnetic field strengths.
A conventional HTSC for magnet construction has a band shape, in particular with rectangular cross-section. It is relatively easy to produce and process.
A major problem in magnet construction is the transition points points) from one superconducting conductor section to another. These joints cannot usually be exposed to the same high magnetic field strengths as the other conductor sections. For this reason, one tries to locate the joints far away from the center of the magnet coil in a region of low magnetic field strength.
This may be difficult to realize when it is geometrically not possible (or undesirable for other reasons) to guide the band-shaped superconductor tangentially away from the coil winding (i.e. tangential to the surface of the cylindrical coil body and approximately perpendicular to the cylinder axis) due for example to the presence of radially outer coil sections which axially project beyond the coil winding in solenoidal coils.
When ductile flexible superconducting wires are used, the conductor can be bent relatively sharply at the end of a winding section of a solenoidal coil winding and extend through arbitrary distances away from the coil winding in the axial direction. A joint can therefore be disposed at a location having practically no magnetic field.
High-temperature superconductors (and other inflexible superconducting materials) do not permit such sharp bends. For solenoidal HTSC coil windings, the joints must be disposed at the upper or lower edge of the coil winding where there are still considerable magnetic fields which are, however, at least lower than in the central region of the coil winding. The superconducting conductor section connected to the solenoidal coil winding at such a joint is then guided out of the region of high magnetic field strength parallel to the cylinder axis of the coil body, (see Haeβner, loc. cit.). These joints at the edge of the coil winding limit the efficiency of the overall magnet coil for many applications.
U.S. Pat. No. 3,559,128 describes a magnet coil having a band-shaped superconductor wound about a cylindrical winding body. The band-shaped superconductor is thereby transferred from a state wherein it seats flatly on the winding body and extends in a peripheral direction to a state in which it is parallel to the longitudinal axis of the winding body and separated from an outer side of that body. The band-shaped superconductor is thereby bent.
U.S. Pat. No. 5,387,891 discloses a magnet coil having a band-shaped conductor containing superconducting filaments. One end of the band-shaped conductor is twisted about a longitudinal axis thereof.
U.S. Pat. No. 4,270,112 discloses a normally conducting or superconducting magnet coil having a conductor with nearly square cross section. The conductor is embedded in a tube-shaped holding cylinder. One end of the conductor is bent, without twisting, through an angle of 90° relative to the peripheral extension of the windings so that the end of the conductor travels parallel to the axis of the cylinder. The holding cylinder is hollow and suitable for holding a coolant.
It is the underlying purpose of the present invention to propose a travel path for inflexible, band-shaped superconductor material, in particular, HTSC material, which permits conductor guidance to or from such a solenoidal coil section in an axial direction under compact construction, without joints to thereby increase the efficiency of a high-field magnet coil.